In recent years, in the dry etching process for high quality thin film formations or fine patterns, the ultrapurification of the process atmosphere, i.e. the technique of supplying ultrapure gases to process apparatuses has become very important.
For instance, in the case of semi-conductor devices, to increase the integrity of integrated circuits, the dimension of unit elements has diminished year after year; in order to practidalize semi-conductor devices of 1 micron to the size of submicron, or even smaller than 0.5 micron, research and development are being actively undertaken. The manufacture of this kind of semi-conductor device is carried out by means of repeating formations of thin films and etching these thin films into specific circuit patterns. Then, this kind of process is usually done by putting the silicon wafer in a process reaction chamber and in a reduced pressure atmosphere infused with specific gases. The purpose of putting it in a state of reduced pressure is to control the etching of through holes or conduct holes with high aspect ratio, to lengthen the mean free path of gas molecules for cave filling, and to control gas phase reactions.
If impurities are introduced into the reactive atmosphere during these processes, some problems will result: the degradation of the quality of thin films, incapability to attain accuracy of fine process, a great selective ratio of etching among different materials, and lack of adherence among thin films. In order to fabricate the integrated circuit, having patterns of submicron or low submicron, in high density and high yield on a wafer of large diameter, it is essential to completely control the reactive atmosphere contributing to the formation of thin films and etching. This is the reason why supplying ultrapure gases has become very important.
Gases used in the manufacturing device of semi-conductors include comparatively stable normal gases (N.sub.2, Ar, He, O.sub.2, H.sub.2) and special material gases possessing properties of strong toxicity, self-sustained combustion, and corrosion (AsH.sub.3, PH.sub.3, SiH.sub.4, Si.sub.2 H.sub.6, HCl, NH.sub.3, Cl.sub.2, CF.sub.4, SF.sub.6, NF.sub.3, WF.sub.6, etc.). As normal gases are easier to handle, they are almost always directly introduced by pressure from the purifying device to the semi-conductor manufacture device. Therefore, through the development and improvement of storage tanks, purifying devices, and piping materials, supplying ultrapure gases to semi-conductor manufacturing devices has become possible. (Ohmi Tadahiro, "A challenge to ppt--a challenge to the concentration of impurities approximating ppt by the gas piping system for semi-conductors." Nikkei Microdevice. July 1987, pp. 98-119.) On the other hand, for special material gases, as careful attention is needed in handling them, the quantity used is very small in comparison to normal gases; therefore, gases in the cylinder are introduced by pressure to the semi-conductor manufacturing device through a cylinder-cabinet piping device.
Up to now, the most serious problem in the ultrapurification of gases supplied from the cylinder through the cylinder-cabinet piping device is the dirt inside the cylinder itself, the existence of large external leakage in the joint of the cylinder-valve and the cylinder, as well as pollution caused by productive absorbing gases, which are engendered because the inside of the cylinder is not accessible to cleaning. However, this problem is also almost overcome by treating the inside to become a specular surface of no processing deterior layer by means of complex electropolish, and the development of cylinder-valves having external threads and which use MCR (Metal C Ring fitting) with built-in purge valves (Ohmi Tadahiro, Murota Junishi. "Technique of Cleaning Bombs and Filling Gases." The Sixth VLSI Ultracleaning Technology--Symposium. A Collection of Drafts "High Performance Process Techniques III." January 1988, pp 109-128). In addition, all the pipelines of the cylinder-cabinet piping device which contains the gas cylinder and supply process gas are double sealed against the atmosphere; moreover, the purge gas supply pipes are devised in a structure purgeable at any time; the realization of such devices to suppress the pollution caused by the entrance of the atmosphere into the pipeline system or by gases chiefly released from water moisture in the internal walls of the pipeline material makes the supply of ultrapure gases possible.
In general prior art, when one kind of gas is supplied to one process apparatus from one gas cylinder, there are few problems because the purging gas supplied to the cylinder-cabinet pipeline device purges the process gas supply pipeline as well as the process gas supply and control pipeline in the process apparatus. However, when using a device for various gases (e.g. reactive ion, etching device (RIE), electronic cyclotron resonance device (ECR), low pressure chemical vapor deposition device (LPCV)), one kind or several kinds of process gases must be selected and mixed from the various process gases before transporting them to the process device. Under this circumstance, when selecting and mixing process gases, if some process gas is left behind in the process gas supply and control pipeline, then replacement of process gas will not take place in that part, hence reducing the degree of purity of the process gas to be supplied to the process device. Besides, although there is no problem concerning the process gas supply and control pipeline when it is used to supply process gas to the process device, the process gas supply and control pipeline is oftentimes in a state of sealing in gases when it is not used to supply process gas; therefore, it will be polluted by the gas chiefly released from water moisture in the inside of the pipeline; and when the process gas supply and control pipeline is used again, this will become the reason for the reduction in the degree of purity of the process gas supplied.
In this way, if the flowing of gas stops and residual gas exists in the gas piping system, it occurs to pollute the piping system and to reduce the purity of the supplied gas. As a result, the process will be tremendously affected.
For instance, the most recently developed DC-RF coupled mode bias sputtering device can also obtain an excellent Al thin film of specular surface with entirely no hillock, even after a heat treatment of 400.degree. C. (T. Ohmi, H. Kuwabara, T. Shibata and T. Kiyota. "RF-DC Coupled Mode Bias Sputtering for ULSI Metalization." Proc 1st Int. Symposium on UltraLarge Scale Integration Science and Technology. May 10-15, 1987. Philadelphia; and Ohmi Tadahiro. "Thorough Elimination of Impurities, Grasping the Conditions for Al Film Formation Without Hillocks." Nikkei Microdevice. October 1987, pp. 109-111). When Al film is formed using this device, it is understood that only when the amount of water moisture contained in Ar is suppressed to below 10 ppb, then the optimum manufacturing conditions for Al film formation can be found out. If Ar Sputter atmosphere contains more than 10 ppb of water moisture, the morphology on the surface of the Al film will degrade. Under this circumstance, the parameter of Al film formation with the resistivity equals to Al bulk and without hillocks after being subject to heat treatment is impossible to be obtained.
In addition, in the method of reducing pressure CVD, if ultrapure SiH.sub.4, H.sub.2, and N.sub.2 containing less than 10 ppb of water moisture are used to engage in thin film formation, and when the absorbing water on the surface of the wafer is suppressed to become very small in quantity, even when under the practical conditions (temperature: 650.degree. C., pressure: a few Torr) wherein there was previously no selective growth nor epitaxial growth in the thin film formation, selective growth and epitaxial growth can be seen. That is, the epitaxial growth of Si on clean Si surface can also be obtained; the film formation of polysilicon above SiO.sub.2 can be suppressed to very few (Murota Junichi, Namamura Naoto, Kato Manabu, Mikoshiba Nobuo, and Ohmi Tadahiro. "An Ultracleaning CVD Technique Having High Selectivity." The Sixth ULSI Ultracleaning Technology--Symposium. A Collection of Drafts "High Performance Process Techniques III." January 1988, pp. 215-226).
FIG. 31(a) through (c) is a most preferred embodiment of the known gas supply pipeline of the process apparatus which supplies a number of process gases to the process apparatus.
A brief description of the above is given with reference to FIG. 31(a). For simplicity sake, FIG. 31(a) shows three kinds of process gas are supplied to the process gas supply piping device for the process apparatus. In FIG. 31(a), 601 is the reaction chamber of the process apparatus, which is connected with the vacuum exhaust device. 608, 609, 610, 614, 615, 616, 617, 618, 619, 629, 630, 631, 632, 633, 634, 635, 636, 637, 643, 644, 648, 649, 650, 652, 653, 654, 658, 659, and 663 are stop valves; among these, 614 and 617, 615 and 618, 616 and 619, as well as 653 and 654 are respectively 3-way dual valves integrating two valves into one. 602, 603, and 604 are process gas supply pipelines, which usually carry the process gas filled in the cylinder or gases for purging pipelines (e.g. Ar) from the cylinder-cabinet pipeline device to the process device pipelines. 611, 612, and 613 are pressure regulators. 620, 621, and 622 are mass flow controllers. 623, 624, and 625 are gas filters. 655 and 660 are spiral pipes for preventing the entrance of atmosphere by reverse diffusion through the blowoff opening for purge gases. 656 and 661 are needle valves for controlling the flow of purge gases. 657 and 662 are floater flow meters. Pressure regulators 611, 612, and 613, mass flow controllers 620, 621, and 622, and gas filters 623, 624, and 625, all these constitute the process gas control pipelines. The number of process gas control pipelines is the same as that of the process gas supply piping lines. 638, 639, 645, 646, and 647 are process device piping lines, the piping system introducing process gas to the process device. 626, 627, and 628 are bypass lines, 640, 641, 642, and 651 are the exhaust pipelines for purge gas and vacuum exhaust pipelines of gas piping, 605 and 606 are purge gas exhaust pipelines, 607 is a vacuum exhaust pipeline, these are severally connected to the exhaust duct or the exhaust device. Generally, these piping lines are composed of 1/4" electropolished SUS 316L pipes.
Next, the function and the operation of the apparatus shown in FIG. 31 (a) are described with reference to FIG. 31 (b) through (f). Here, the supply of process gas from the process gas supply piping line 602 to the reaction chamber 601 is used as an example, and its operation is separately explained in points (1) to (5).
(1) When the Device Stops
As a general rule, when the process device is not used for the process gas, as shown in FIG. 31 (b), and when stop valves 608, 609, 610, 614, 615, 616, 617, 618, 619, 629, 630, 631, 635, 636, 637, 643, 644, 648, 649, 650, 654, 658, 659 and 663 are all in an open state, and stop valves 632, 633, 634, 652 and 653 are all in a closed state, the purge gas (e.g. Ar) passes from the process gas supply piping lines 602, 603, and 604 through needle valves 656 and 661 for flow regulation to the front of the reaction chamber of the process device; and all this time the purge gas inside the piping system is constantly flowing. The thick lines represent the flow of the gas.
(2) When Process Gas Is Substituted for Purge Gas
Next, in order to supply ultrapure process gas to the process apparatus, the operation of substituting the residual purge gas (e.g. Ar gas) in the supply piping system with process gas is carried out. First of all, from the state as shown in FIG. 31(b), close valves 658, 663, 654, 656, 659, and 661, then close valves 635, 636, 637, 649, and 650, and stop the supply of purge gas (e.g. Ar) from the process gas supply piping line 602. Subsequently, open valve 653, the process gas passes through the reaction chamber 601 to proceed with the vacuum exhaust discharge in process gas supply pipelines 638, 639, 645, 646, and 647; open valves 632 and 652, and use the vacuum exhaust pipeline 607 to engage in vacuum exhaust discharge in piping lines 626 and 640 as well as the piping lines of the cylinder-cabinet piping device (FIG. 31(c)). And valve 635 is in its original close state. After the degree of vacuum inside the piping lines reaches a degree of, say, 1.times.10.sup.-2 Torr, close valves 648 and 653. Then, open valve 635, and supply process gas from the process gas supply piping line 602 to fill the piping system with process gas (FIG. 31(d)). Next, stop the supply of process gas, open valves 648 and 653, and allow vacuum exhaust discharge, the same vacuum exhaust discharge for purge gas, to take place in the piping system (FIG. 31(c)). This supply of process gas from the process gas supply pipeline 602 and the vacuum exhaust discharge in the piping lines are generally repeated more than five times, and then close valves 608, 614, 617, 629, 632, 643, 644, 648, and 653.
(3) The Supply of Process Gas
After the above-mentioned operation, with valves 608, 617, 635, 643, 644, and 653 in their open state, regulate the supply pressure and flow of process gas by means of the pressure regulator 611 and the mass flow controller 620 and supply the process gas to the reaction chamber 601. Then close valve 652, open valves 649, 650, 659, 661, and 663, and begin anew the purging of piping lines 603 and 604, which have not supplied process gas. This state is as shown in FIG. 31(e).
(4) Stopping the Supply of Process Gas
Following, the method of stopping the supply of process gas is described. This operation is similar to that of the supplying process gas; not that process gas will substitute for purge gas, but that purge gas (e.g. Ar) will substitute for process gas. The supply of purge gas and the vacuum exhaust discharge in the piping lines are usually repeated more than five times in this operation. Then, close valves 608, 614, 617, 629, 632, 635, 643, 644, 648, 652, and 653, and supply purge gas from the process gas supply piping line 602. Next, open valves 608, 614, 617, 629, 635, 643, 644, 648, 654, 656, 658, 659, 661, and 663, and begin purging (FIG. 31(f)). When purging starts again from the system of piping lines 603 and 604, the state shown in FIG. 31(b) is obtained.
However, although, in the apparatus shown in FIG. 31(a), for instance, when process gas from the process gas supply pipeline 602 is supplied or checked, the substitution of purge gas with process gas or the substitution of process gas with purge gas is taking place. At this time piping lines 627, 641, 628, and 642 in the other cylinder gas cabinet piping devices 603 and 604 should allow no passage of purge gas, and they should be completely closed (FIGS. 31(c) (d)). Furthermore, when the process gas supply piping line 602 is supplying process gas, though purge gas is flowing in the piping system of the process gas supply piping lines 603 and 604, piping lines 626 and 640 for discharging exhaust of purge gas of the process gas supply piping line 602 and for vacuum exhaust discharge of the gas pipelines must be thoroughly closed (FIG. 31(e)). In this way, under the condition that the gas supply piping system is completely closed, the inside of the system will be contaminated by gas released chiefly from water moisture in the inner walls of the piping material.
FIG. 32 shows the dew point change in this kind of gas piping system when the system is practically sealed. In the system wherein the dew point has already been lowered to -98.degree. C. by means of subjecting the supply piping system to baking or the like, under the condition that gas is reintroduced 9 days after stopping the supply of gas, the dew point of the gas will rise to -42.degree. C., and 3 days are needed for it to resume its former value. Therefore, closing the gas supply piping system will pollute the inside of the piping system, hence becoming a big problem for the process apparatus of the gas supply system which requires ultrapure gases.
Furthermore, in the apparatus shown in FIG. 31(a), when supplying process gas from process gas supply piping line 602 (FIG. 31(e)), process gas supply piping lines 638 and 639 of the process gas supply piping lines 603 and 604 will become the dead zone for the gas, and hence no exchange of gas can take place, causing the reduction of the purity of the process gas supplied. Moreover, when supplying process gas from the process gas supply piping line 604, not only the piping lines 628 and 642, which are used for exhaust discharge of purge gas and vacuum exhaust discharge of the gas pipelines, but the process gas supply piping lines 638, 639, 645, and 646 are also closed; therefore, the pollution inside the pipelines becomes more severe (FIG. 31(g)). The known technique as described above illustrates the situation wherein there are three process gas supply piping lines; in real installation, the number is much greater, and hence the effect of pollution becomes worse.
Therefore, for a piping system which supplies a number of process gases to one single process apparatus, it is hoped that there is a systematic technique wherein purging and vacuum exhaust discharge can take place independently in each process gas supply pipeline and each piping line of the process apparatus, no dead zone of gas is created in the confluent part of each process gas supply piping line, and purge gas can be flowed continuously through an unused piping system.
In view of the above, the primary object of the present invention is to offer a gas supply piping system for a process apparatus of a structure wherein, when supplying a number of process gases to a process apparatus, residence of gas is completely absent in the piping system, and purging as well as vacuum exhaust discharge can independently proceed within each process gas supply piping system.